Due to integration of a semiconductor device and narrowing of a process margin involved in that, the need for two-dimensional dimension measurement such as a contact hole and a wiring pattern in addition to the prior-art line and space measurements (one-dimensional length measurement) is increasing for a testing/measuring device on the basis of a scanning electron microscope which observes a superfine pattern.
However, in the prior-art technologies, when a fine pattern formed of an insulating material such as resist or SiO2 is subjected to SEM observation, the profile line intensity of the pattern depends on the electron scanning direction (the intensity of the pattern edge parallel with the electron scanning direction is lowered). This is caused by the fact that the sample is charged by electron irradiation, and thus, shape distortion or uneven brightness occurs in an image. FIG. 1 shows an example of an electron scanning method in a view field when an image is obtained. An image of the resist pattern (FIG. 2(a)) obtained by this scanning method is shown in FIG. 2(b). The profile line intensity of the edge of the resist and the line profile depend on the electron scanning direction, and the profile line (parallel edge) in parallel with the electron scanning direction might be lost in some cases. If a pattern profile line is extracted by using this image, a defect (pattern outline loss) or an erroneous extraction (occurrence of ghost, that is, a line is detected where there should not have been a pattern) might occur in the profile data as illustrated in FIG. 2(c). As a result, measurement of the original processed dimension or shape of the pattern on the sample on the basis of profile line information becomes difficult.
The causes for that include the fact that the charged state on the sample surface is different depending on the relative direction of electron scanning and the pattern edge. As illustrated in FIG. 3, if electrons are made to scan in parallel with the pattern edge (FIG. 3(a)), positive charging produced by the previous scanning line is stronger than the perpendicular scanning case (FIG. 3(b)), and probability of return of the secondary electrons generated by electron beam irradiation to the sample surface becomes high. As a result, the profile line intensity on the image is reduced, the profile of the pattern cannot be extracted and the dimension or shape measurement of the pattern is obstructed.
In order to suppress the above obstruction, the influence of the electron-beam irradiation charging needs to be suppressed. Conventionally, in order to suppress the charging caused by electron irradiation, the following methods have been disclosed. For example, Patent Literature 1 describes that an inactive gas is introduced into the vicinity of the sample and ionized by primary electron irradiation, and the charging generated on the sample surface during image taking is neutralized. Patent Literature 2 describes that irradiation charging is neutralized by a flood gun or primary electron beam (irradiation energy different from that in image taking) examination between frames in the image taking. Patent Literatures 3, 4, and 5 describe that the influence of irradiation charging is suppressed by controlling the scanning direction of the electron beam so that the primary electron beam scans the pattern edge perpendicularly or diagonally. Moreover, Patent Literature 6 describes a method of optimizing the scanning interval of the primary electron beam in the view field for each observation sample.